The invention relates to a time division multiplex (TDM) switching network having switching units which, through time position conversion, cause mutual allocation time slots formed on connected TDM lines.
TDM switching networks wherein the switching between time slots formed on the connected TDM lines takes place only through time position conversion by means of appropriate timing circuits are old in the art, as exemplified in West German Offenlegungsschriften 2 025 102 and 2 064 202.
These prior art TDM switching networks have the configurations of conventional space division multiplex switching networks which are based on a three-stage basic design. With a greater number of terminals for TDM lines, one changes over to switching arrangements having a still greater number of stages (e.g., five stages). However, this case involves a huge expansion step, for example, leading from 16,000 to 500,000 simultaneously possible connections.
Therefore, if the expansion is to be effected in smaller steps, the three-stage basic design is adhered to and the original switching network is double (West German Offenlegungsschrift 2 064 202). However, to achieve this, it is necessary that the timing circuits located in the intermediate switching network stage be designed for the connection of still a greater number of links than are necessary for the simple basic switching network whereby, in the interest of providing for expansion possibilities, the greater number of link terminals is provided in advance.
With regard to the feasibility of constructing the switching units as integrated circuits, it is of interest to work with switching units of but one basic design. However, it is of interest to have switching units having only a small number of line terminals. Generally speaking, it is also of interest to have a switching network design that may be used uniformly for all the sizes of the switching network and which allows the switching network to be expanded in small steps.